Electroplated member and method and apparatus for electroplating

ABSTRACT

Method and apparatus for electroplating a uniform metallic film on a substantially flat platable surface of a member to be plated. A container for an electrolyte solution has an interior nonconductive surface defining a predetermined cross section for containing an electrolyte solution. A holder has a platable surface and mounts the member such that the flat surface of the member forms part of a larger platable surface with the holder. The larger platable surface is mounted in the container at a right angle to the nonconductive surface and extends over substantially all of the predetermined cross section of solution.

United States Patent [72] Inventor John P. Faulkner Thousand Oaks, Calif.

[21] Appl. No. 34,507

[22] Filed May 4, 1970 [45] Patented Jan. 11, 1972 [73] Assignee Burroughs Corporation Detroit, Mich.

Continuation of application Ser. No. 253,859, Jan. 25, 1963, now abandoned and a continuation-in-part of 659,546, Aug. 9, 1967, now abandoned. This application May 4, 1970, Ser. No. 34,507

[54] ELECTROPLATED MEMBER AND METHOD AND APPARATUS FOR ELECTROPLATING 75 Claims, 13. Drawing Figs.

[52] U.S. Cl 29/194, 204/23, 204/237, 204/263, 204/297 R [51] Int. Cl 323p 3/00, C23b 5/00, BOlk 3/00 [50] Field of Search 204/23, 27, 235-239, 263, 261, 264, 287, 297

[56] References Cited UNITED STATES PATENTS 2,044,431 6/1936 Harrison 204/23 2,048,578 7/1936 Van Der Horst 204/27 2,675,348 4/1954 Greenspan 204/297 2,526,951 10/1950 Kiefer, Jr 204/140.5 3,006,837 10/1961 Pennington 204/280 1,830,343 11/1931 Udy 204/297 2,149,344 3/1939 Hull 204/23 OTHER REFERENCES Current and Metal Distribution by H. L. Pinkerton, pgs. 480- 490, Electroplating Engineering Handbook 2nd Ed.

Current Distribution and Throwing Power in Electrodeposition pgs. 313- 345, by H. E. Haring et :11. From Paper Presented at 43rd General Meeting of A.E.S. May 23, I923.

The Theory of the Potential and the Technical Practice of Electrodeposition, pgs. 131- 161, by Charles Kasper From paper presented at 78th General Meeting of the A.E.S. Oct. 4, 1940.

The Theory of the Potential and the Technical Practice of Elecrodeposition, pgs. 353- 383, by Charles Kasper, from paper presented at the 77th General Meeting of A.E.S. April 27, 1940.

Primary Examiner-John H. Mack Assistant ExaminerT. Tufariello AttorneyChristie, Parker & Hale mined cross section of solution.

PAIENTEDJAH 1 1 I972 SHEET 2 OF 7 INVENTOR PATENTEDJAH 11 I972 3, 34, 47

sum 5 0r 7 F/E 5 I 2W llllllllll I lllllllllllll I L I I F l PATENTEDJAH 11 I972 I 3, 34,947

sum 7 n5 7 ELECTROPLATED MEMBER AND METHOD AND APPARATUS FOR ELECTROPLATING This application is a continuation of the now abandoned copending application bearing Ser. No. 253,859, filed Jan. 25, l963, entitled METHOD AND APPARATUS FOR ELEC- TROPLATING, and assigned to the same assignee as the present application, and a continuation-in-part of the now abandoned copending application bearing Ser. No. 659,546 filed Aug 9, 1967 entitled METHOD AND APPARATUS FOR ELECTROPLATING and assigned to the same assignee.

The present invention is directed to improvements in electroplated members and in the method and apparatus for electroplating and, more particularly, to a method and apparatus for electrodepositing thin metallic films having uniform thickness and magnetic properties and a member electroplated using such method and apparatus.

In electronic systems, such as high-speed data-processing systems and the like, it is common to employ magnetic recording apparatus for receiving and recording coded information. One form of magnetic recording apparatus presently employed in such systems includes one or more discs having magnetic recording surfaces for storing coded information. It is desired that the magnetic discs be capable of storing large quantities of digital information in a small area, i.e., that the discs be capable of high-density magnetic recording. To record large quantities of information on a disc however it is necessary that the recording surfaces of the disc have a consistent thickness and magnetic properties as well as a high order of mechanical perfection over its entire recording area.

Heretofore it has been extremely difficult to meet the above requirements using conventional electroplating methods and apparatus. This is primarily due to the difficulty of maintaining constant current densities over the entire plating surfaces of the disc during electroplating. In particular, since the thickness of an electrodeposit at any point on a platable surface is proportional to the time integral of the current at the point and since the magnetic properties of a deposit vary somewhat with the current density developed during electroplating, the lack of close control over current density in conventional electroplating apparatus has made the plating of magnetic surfaces capable of high-density recording extremely difficult.

In view of the above, the present invention provides an improved electroplated member and an improved electroplating method and apparatus which maintains an essentially uniform current density over the entire plating surface ofa member to be plated to produce a magnetic film having uniform thickness and magnetic properties. In addition, the present invention maintains a constant volume of clean electrolyte in contact with the platable surfaces of the member to be plated to provide means for depositing a film having a high degree of mechanical perfection over the entire platable surface of the member to be plated.

Briefly, an embodiment of the invention comprises a member having a metallic film of unifomi thickness and magnetic properties electrodeposited on a flat platable surface thereof. The electrodeposition is made in a fluid electrolyte solution contained so as to have a predetermined cross section in size and shape while the member is mounted on a holder therefor having a platable surface. The surfaces of the holder and member form part of a larger platable surface extending over substantially all of the cross section of solution while a uniform electric field is generated through the solution up to the larger surface. A preferred embodiment of the invention is a member so electroplated while mounted in an opening of a holder allowing the platable surfaces of the member and holder to form a larger substantially continuous flat surface.

An embodiment of the present invention is a process for electroplating a metallic film of uniform thickness on a flat platable surface of a member. The member is positioned in a holder having platable surfaces such that the platable surface of the member effectively forms a portion of a larger platable surface with the holder. The larger platable surface is immersed in an electrolyte solution which is contained within a predetermined cross section such that the larger platable surface extends over substantially all of said cross section. A uniform electric field is generated through the electrolyte solution up to and normal to substantially all of said larger platable surface. A preferred embodiment of the invention involves the step of positioning the member in an opening of a holder so that the platable surface of the member effectively forms part of a larger flat, substantially continuous platable surface with the holder. A preferred embodiment involves a process for simultaneously electroplating opposing substantially flat platable surfaces of a member by positioning the member in a holder having opposing substantially flat platable surfaces so that the opposing surfaces of the member each effec'tively form part of larger flat surfaces with the opposing surfaces of the holder. Both larger surfaces extend over substantially all of the cross section of solution and are simultane ously electroplated.

Briefly, apparatus in accordance with the present invention for electroplating a uniform film on a substantially flat platable surface of a member includes a container having an interior nonconductive surface for containing an electrolyte solution in a substantially constant cross section in between first and second electrode positions. First and second substantially parallel electrodes are respectively positioned at the first and second positions and extend substantially nonnal to the nonconductive surface over substantially all of said cross section, thereby enabling a substantially uniform electric field to be generated throughout the solution between the electrodes. A platable holder is constructed for mounting the member and has a substantially flat electroplatable surface. The surfaces of the holder and member are electrically connected together and comprise the first electrode. in a preferred embodiment the holder has an opening for receiving the member which allows the surfaces to be positioned in the same plane. Also, in a preferred embodiment the member has opposing electroplatable surfaces as does the holder so that the opposing surfaces can be simultaneously electroplated. A preferred embodiment has a holder including a removable adapter to adapt a member of different peripheral configuration or thickness to the configuration of the opening or the thickness of the holder.

A subcombination of the invention comprises the aforementioned apparatus in the absence of the member to be plated.

in the disclosed embodiment of the invention a metallic disc is mounted within a holder member having a flat platable surface continuous with and surrounding the flat platable surface of the disc. The disc thus secured is immersed in an electrolyte solution containing ions of the metal to be plated preferably by passing clean electrolyte solution over a major portion of the flat continuous surface including the entire platable surface of the disc. A uniform electric field is then developed through the electrolyte solution normal to the continuous flat surface of the holder member. Since the electric field is normal to the flat surface of the holder member and since the flat surface of the holder member is continuous with and surrounds the flat platable surface of the disc, the platable surface of the disc defines an equipotential surface normal to the electric field on which the current density is everywhere constant. Since the current density is uniform over the flat platable surface of the disc, the metallic deposit thereon has the uniform thickness and magnetic properties required for highdensity magnetic recording. in addition, since in the preferred form of the invention clean electrolyte solution is continuously passed over the continuous flat surface of the disc and holder member, relative movement is provided between the platable surface of the disc and the solution to prevent colloidal particles from contacting the surface. Therefore, the metallic deposit has a high degree of mechanical perfection over the entire platable surface of the disc.

More particularly, to develop the uniform electric field which is everywhere normal to the platable surfaces of the disc, the apparatus of a preferred form of the present invention includes a tank having opposing parallel walls formed of a nonconductive material. The holder member, including the disc, is mountable within the tank to extend between and substantially normal to a pair of opposing walls. Mountable on one side of the holder member within the tank is a porous diaphragm member. The diaphragm member extends between and substantially normal to the pair of opposing walls and is composed of a nonconductive material insoluble in the electrolyte solution to be disposed within the tank.

Positioned on a side of the diaphragm member remote from the holder is an electrode assembly having a flat electrode surface extending between and substantially normal to the opposing walls of the tank. The electrode assembly is connected as an anode while the holder member is connected as a cathode by means external to the tank.

Clean electrolytic solution containing ions of the metal to be plated is pumped into the tank through an opening in the base of the tank along the holder member. The clean electrolytic solution flows upward over the flat continuous surface of the holder member between the holder member and the diaphragm member. The electrolytic solution also flows through the diaphragm member and over the top of the diaphragm members into the region of the electrode assembly. The electrolytic solution fills the area around the electrode assembly and flows from the tank through outlet ports adjacent the electrode assembly at a height slightly lower than the height of the diaphragm as mounted within the tank.

Due to this arrangement a constant volume of clean electrolyte solution continuously immerses the entire platable surface of the disc and the major portion of the platable surface of the holder member.

Since the electrode assembly and the holder member are substantially parallel to each other and normal to the sidewalls, they combine with the sidewalls to form a substantially rectangular structure. Further, the electrode assembly and the holder member each have an equal surface area exposed to the electrolyte solution. Therefore, a nearly parallel electric field is developed between the electrode assembly and the holder member through the pores in the diaphragm member. The uniform electric field is normal to the holder member and thus everywhere normal to the platable surface of the disc enclosed therein. Thus, in electroplating with the apparatus of the preferred form of the present invention, the metallic film deposited on the platable surface of the disc has a uniform thickness and magnetic properties. Also, since a constant volume of clean electrolytic solution is continuously in contact with the platable surface of the disc the metallic deposit is free from colloids and other particles which may produce a roughness of the surface of the deposit.

The above, as well as other features of the present invention, may be more clearly understood by reference to the fol lowing detailed description when considered with the drawings, in which:

FIG. 1 is a sectional end view of a preferred form of the electroplating apparatus of the present invention;

FIG. 2 is a top view of the electroplating apparatus illustrated in FIG. 1;

FIG. 3 is a sectional side view of the portion of the electroplating apparatus for supplying clean electrolytic solution to the tank illustrated in FIG. 1;

FIG. 4 is a schematic representation of the holder member supporting a disc;

FIG. 5 is a schematic representation of the electrical wiring arrangement associated with the electrode assemblies for plating on both side of the disc;

FIG. 6 is a schematic representation of an alternate holder member having an adapter and supporting a disc with a plug for use in the apparatus of FIG. 1;

FIG. 7 is an enlarged view of the adapter, disc and plug assembly shown in FIG. 6;

FIG. 8 is an enlarged section view of the adapter and disc of FIG. 7 taken along the lines 8-8 and showing a portion of the outer portion of the holder in which the adapter is mounted;

FIG. 9 is a schematic representation of an alternate electroplating apparatus and embodying the present invention;

FIG. I0 is a cross-sectional view of the electroplating apparatus of FIG. 9 taken along the lines l0-- I0;

FIG. I I is a schematic representation of an alternate holder and disc for use in the electroplating apparatus of FIGS. l and 9 and embodying the present invention;

FIG. 12 is a section view of the holder and disc assembly shown in FIG. 11 taken along the lines l2l2; and

FIG. 13 is a schematic and block diagram of an electrical circuit for applying plating current between electrodes in the electroplating apparatus of FIGS. 1 and 9.

As represented in the drawings, the preferred form of the electroplating apparatus of the present invention includes a tank 10 composed of a nonconductive material such as polyester-reinforced fiberglass. The tank 10 includes opposing sidewalls l2 and 14, opposing end walls 16 and I8, and a bottom member 20. The opposing sidewalls, as well as the opposing end walls, are substantially parallel to each other and normal to the bottom member 20. The bottom member 20 includes an elongated opening 22 which extends between the sidewalls l2 and 14. The opposing end walls 16 and 18 include elongated ports 24 and 26, respectively, which extend along the end walls adjacent the top of the tank. The ports 24 and 26 open into flumes 28 and 30, respectively, which are molded to and form a part of the outer surface of the end walls I6 and 18. The flumes 28 and 30 provide means for transporting electrolytic solution from the tank to a storage vessel (not shown).

Extending upward within the end walls 12 and I4 in line with the elongated opening 22 are a pair of central slots 32 and 32. The central slot 32 extends downward within the sidewall 12 from the top of the tank 10 to a point slightly above the elongated opening 22 while the slot 32' extends within the sidewall 14 from the top of the tank to a similar point slightly above the opening 22. The upper ends of the slots 32 and 32' are tapered outwardly toward the opposing sidewalls 16 and 18 to provide means for receiving and supporting a holder member 34.

As most clearly illustrated in FIGS. 1 and 4, the holder member 34 is a substantially rectangular plate having an enlarged upper portion to provide a hand-gripping area 35. The holder member 34 is composed of a platable material which is cleanable by the same processes required to cleanse the member to be plated by the electroplating apparatus. By way of example only, when a brass disc such as illustrated at 36 is to be plated the holder member 34 may be copper. The holder member 34, as illustrated, includes a pair of opposing substantially flat platable surfaces 38 and 40. The holder member 34 also includes an opening 42 for receiving the member to be plated, in this case the disc 36. The disc 36 also includes a pair of opposing substantially flat platable surfaces 44 and 46. The holder member 34 is arranged such that when the disc 36 is mounted within the opening 42 the flat platable surfaces 38 and 40 form substantially continuous flat platable surfaces with the platable surfaces 44 and 46, respectively.

To provide means for clamping the disc 36 within the holder member 34 to extend substantially normal to the sidewalls I2 and 14, a pair of flat extremely thin ring members 48 and 50 are positioned to overlap the edge of the disc 36 and the opening 42 in the holder member 34, as illustrated. The ring members 48 and 50 are also composed of copper and are secured to the holder member 34 by a plurality of small copper screws such as 52 which extend into the holder member substantially flush to the outer surface of the ring members such as 48.

The disc 36 may also include a central opening 54. To enclose the central opening 54 a flat plug element 56 is shaped to fit within the opening 54 and to extend substantially flat platable surfaces along the opposing surfaces of the disc 36. The plug 56 is also composed of a metal such as copper which is subject to the same cleansing procedures as the brass disc.

To clamp the plug element 56 within the opening 54 a pair of flat copper ring members extend over the opening 54 to overlap slightly the opposite surfaces of the disc 36 around the opening 54. The pair of ring members 58 and 60 are extremely thin and are coupled to the plug element 56 by a plurality of copper screws such as 62 which extend into the plug element 56 substantially flush with the outer surface of the ring 58.

Since the ring members and screw elements provided for clamping the disc 36 within the opening 42 in the holder member 34 are extremely thin and protrude only slightly from the otherwise continuous platable surfaces they have little, if any, effect upon the uniform plating provided by the electroplating apparatus of the present invention.

Equally spaced on opposite sides of the central slots 32 and 32/ are two pairs of vertically extending slots 64 and 64 and 66 and 66. The slots 64 and 66 extend downwardly in the sidewall 12 from the top of the tank to points immediately adjacent the sides of the slot 22 and are equally spaced from the central slot 32. The slots 64' and 66 extend downwardly in the sidewall 14 and are aligned with the slots 64 and 66, respectively. In particular, the slots 64 and 66 extend from the top of the tank 10 downward to points immediately adjacent the sides of the slot 22 and are equally spaced from the central slot 32'. The upper portions of the slots 64, 64, 66 and 66 are enlarged to receive and support the upper portions ofa pair of diaphragm members 68 and 70 as illustrated in FIGS. 1 and 2.

The diaphragm members 68 and 70 may be composed of any porous material which is relatively tight in structure, nonconductive and insoluble in the electrolyte solution to be disposed within the tank. The diaphragm members 68 and 70 extend from the opposing sidewalls 12 and 14 substantially parallel to the holder member 34 adjacent opposite sides of the elongated opening 22. The diaphragm members are arranged to only pass an electrolyte solution through its pores when a predetermined pressure differential is developed across the diaphragm members. In addition, the diaphragm members 68 and 70 are arranged to extend upward within the tank 10 to a height slightly above the lower surface of the ports 24 and 26 in the sidewalls of the tank 10. As will be hereinafter described, this arrangement of the diaphragm members 68 and 70 prevents the flow of electrolyte solution through the diaphragm members toward the holder member while maintaining a uniform voltage of clean electrolyte solution in contact with the platable surfaces of the disc 36 and holder member 34.

Equally spaced from the slots 64 and 64 and extending from the end wall 16 along the sidewalls 12 and 14 are slots 72 and 72'. The slots 72 and 72' define a well 74 for receiving an electrode assembly 76. The electrode assembly 76 includes metal crossbar member 78 which extends between the sidewalls 12 and 14 over the well 74. The crossbar member 78 is supported on the upper surface of the sidewalls 12 and 14 and is coupled thereto by a pair of screw members 82 and 84 which extend through elongated slots 86 and 88 in the upper surfaces of the crossbar member 78 and into the sidewalls 12 and 14 as illustrated in FIG. 2. By loosening the members 86 and 88 the electrode assembly may be moved toward and away from the holder member 34 to provide selective positioning for the electrode assembly 76 within the well 74.

The crossbar member 78 supports a plurality of flat plate electrodes 90, 92 and 94. The flat plate electrodes are coupled to the crossbar 78 by screw members such as 96 which extend through the flat plate electrode members and into an upwardly extending flange 80 of the crossbar. The flat electrode members 90, 92 and 94 are aligned across the crossbar member 78 side by side and are spaced slightly from each other. By this arrangement the electrode members 90, 92 and 94 extend a substantially flat electrode surface substantially parallel to the holder member 34 and between the opposing sidewalls 12 and 14 of the tank 10.

As represented in FIG. 2, the crossbar member 78 extends beyond the sidewall 12 to receive a connector member illustrated at 98. Coupled to the connector member 98 is a cable 100 for passing electrical current to the electrode assembly 76.

Equally spaced from the slots 66 and 66 and extending from the end wall 18 along the sidewalls 12 and 14 are slots 102 and 102. The slots 102 and 102' define a well 104 for receiving an electrode assembly 106. The electrode assembly 106 includes metal crossbar member 108 which extends between the sidewalls l2 and 14 over the well 104. The crossbar member is supported on the upper surface of the sidewalls 12 and 14 and is coupled by a pair of screw members 111 and 112 which extend through elongated slots 116 and 118 in the upper surfaces of the crossbar member 108 and into the sidewalls l2 and 14 as illustrated in FIG. 2. By loosening the screw members 111 and 112 the electrode assembly may be moved toward and away from the holder member 34 to provide selective positioning of the electrode assembly 106 within the well 104.

The crossbar member 108 supports a plurality of flat plate electrodes 120, 122 and 124. The flat plate electrodes are coupled to the crossbar member 108 by screw members such as 125 which extend through the flat plate electrode members and into an upwardly extending flant 110 of the crossbar. The flat electrode members 120. 122 and 124 are aligned across the crossbar member 108 side by side and are slightly spaced from each other. By this arrangement the electrode members 120, 122 and 124 extend a substantially flat electrode surface substantially parallel to the holder 34 and between the opposing walls 12 and 14 ofthe tank 10.

As represented in FIG. 2, the crossbar member 108 extends beyond the sidewall 12 to receive a connector member illustrated at 128. Coupled to the connector member 128 is a cable 130 for passing electrical current to the electrode assembly 106.

As illustrated in FIGS. 1 and 3, the tank 10 is mounted on a baffle box 132. The bafile box 132 is separated from the tank by a gasket 134 and includes an inlet opening 136 for receiving filtered electrolyte solution. The baffle box 132 also includes a longitudinally extending outlet port 138 for communicating with the opening 22 in the tank 10 through an opening 140 in the gasket 134.

Extending around the opening 136 and longitudinally along the outlet port 138 is a hollow cone member 142. To support the cone member 142 around the opening 136 the cone member includes an outwardly extending flange 144 which is coupled to a sidewall of the baffle box 132 by a plurality of screw members. The cone member 142 includes two groups of outlet ports such as 146 and 148 illustrated in FIG. 1 which opens into the baffle box and faces opposite sidewalls thereof. The outlet ports in each group of ports are aligned with each other and spaced from the opening 136 toward the small end 150 of the cone member 142 which is blocked to fluid flow. The outlet ports are spaced from each other and decrease in radial dimension as they approach the enclosed end 150 of the cone member 142. In particular, the outlet ports are dimensioned such that electrolyte solution flowing through the opening 136 and into the cone member 142 pass through the outlet ports therein with equal velocity irrespective of the displacement of the ports from the inlet opening 136. Thus, the arrangement of the cone member 142 maintains the velocity head of the electrolyte solution pumped into the baffle box 132.

In addition to the cone member 142, the baffle box 132 includes a plurality of baffle members 152, 154 and 156. The bafi'le members 152 and 154 lie in a common plane and extend from opposite sidewalls of the baffle box 132. The baffle members 152 and 154 are spaced from each other to provide an opening 158 for fluid to flow upward within the baffle box 132. The baffle member 156 extends from opposite end walls of the baffle box 132 over the opening 158. By thus positioning the baffle members 152, 154 and 156 electrolyte solution flowing through outlet ports in the cone member 142 passes around the cone member 142 upward through the opening 158 and outward around the baffle member 156. The electrolyte solution then flows upward through the openings 138. 140 and 22 in the tank 10. Due to the arrangement of the baffle members the electrolyte solution reaching the opening 22 has a constant pressure along the opening 22.

The electrolytic solution, in passing from the baffle box 132, enters the tank 10 through the opening 22. The electrolyte solution passes upward on either side of the holder member 34 between the diaphragm members 68 and 70. As the solution rises between the holder member 34 and the diaphragm members a pressure differential is developed across the diaphragm members which allows some of the solution to pass through the pores of the diaphragm members into the regions surrounding the electrode assemblies 76 and 106. The electrolyte solution continues to rise between the holder member 34 and the diaphragm members 68 and 70 to completely immerse the disc 36 and the platable surfaces of the holder member 34. When the solution reaches the top of the diaphragm members 68 and 70 it flows over the top of the diaphragm members and into the regions surrounding the electrode assemblies 76 and 106. The solution then fills the remainder of the tank 10 to a height controlled by the height of the outlet ports 24 and 26. Since, as previously described, the heights of the diaphragms 68 and 70 is slightly greater than the lower surface of the outlet ports 24 and 26, a pressure differential is developed across the diaphragm members which prevents electrolyte solution from flowing through the diaphragm members toward the holder member 34. This maintains a constant volume of clean electrolyte solution in contact with the platable surfaces of the disc and holder members. In addition, since the solution continuously flows upward about the platable surfaces of the disc and holder members, the solution is continuously being agitated relative to the surfaces to be plated. As is commonly known, such agitation is necessary in electroplating processes to prevent gas pitting which produces a roughness of the surface being plated.

The actual composition of the electrolyte solution utilized to plate the platable surfaces of the disc may vary with the desired composition of the metal to be plated on the disc. By way of example only, a typical composition of the electrolyte solution which may be employed in the electroplating apparatus of the present invention is a modified Watts bath comprising 25 grams per liter of cobalt as cobalt sulfate, grams per liter nickel as nickel sulfate, 10 grams per liter nickel as nickel chloride, 12 grams per liter sodium sulfate and 30 grams per liter of boric acid. The temperature of the electrolytic solution may be within the range of 45 to 65 C. and the pH of the solution between 3.5 and 5.0 by the addition of sulfuric acid.

In the electroplating apparatus of the present invention the electrode members of the electrode assemblies 76 and 106 may be composed of various metals or metal compounds. In order to plate out a composition of nickel and cobalt it is preferred that the electrode members be composed of approximately 80 percent cobalt and percent nickel.

To plate a metallic film having a uniform thickness and magnetic properties on the platable surfaces of the disc 36 and holder member 38, the electrode assemblies 76 and 106 and the holder member 34 are electrically connected as illustrated in FIG. 5. In particular, the holder member 34 together with the disc 36 is coupled as a cathode by connecting the holder 34 to the negative pole of a voltage supply represented by the battery [60. The electrode assembly is connected to the positive pole of the battery 160 through a high-resistance element 162 while the electrode assembly 106 is coupled to the positive pole of the battery 160 through a high-resistance element 164. The high-resistance elements 162 and 164 are of equal value. Connected between the high-resistance elements 162 and 164, as illustrated, is a millivolt meter 166. The combination of the highresistance elements and the millivolt meter provides means for insuring an equal displacement between the electrode assemblies and the holder member 34 and that the current density on the opposing platable surfaces of the disc 36 is everywhere equal. To accomplish this the screws holding the crossbar members of the electrode assemblies 76 and 106 are loosened and the electrode assemblies moved within their associated wells until a zero reading results at the meter 166. When this occurs equal currents are flowing through the high-resistance element 162 and 164 and over the opposing platable surfaces of the disc 36 and platable member 34 to insure that the thickness of the metallic film plated on both sides of the disc is equal.

The connection of the electrode assemblies 76 and 106 as anodes and the holder member 34 as a cathode develops an electric field between the electrode assemblies and the holder member 34. Since the fiat platable surfaces of the holder member and disc 36 are substantially parallel to the flat electrode surfaces of the electrode assemblies and normal to the sidewalls 12 and 14, and since the cross'sectional area of the electrolyte solution parallel to the anode and cathode is substantially constant and equal to the exposed areas of the anode and cathode a nearly parallel field results between and substantially normal to the platable surfaces of the disc 36 and holder member 34. Since the platable surfaces of the holder member 34 and disc 36 are normal to the uniform electric field the platable surfaces define equal potential surfaces on which the current is everywhere constant. Since the current is everywhere constant on the platable surfaces of the disc and holder member the metallic deposit on the platable surfaces is everywhere uniform both as to thickness and magnetic properties.

The diaphragm members 68 and 70, in addition to providing means for maintaining a uniform volume of clean electrolytic solution in contact with the platable surfaces of the disc and holder member also aids in the formation of the uniform parallel electric field. In particular, the current passing through the electrolyte solution is conducted through the pores in the diaphragm. To the flat platable surfaces of the disc and holder member, the pores appear as virtual anodes substantially parallel to the platable surfaces of the disc and holder member. These virtual anodes formed by the pores are closely spaced to the surfaces to be plated and effect a redirecting of the electric field normal to the platable surfaces of the disc and holder member.

Thus, in the apparatus of the present invention a uniform electric field is developed normal to the flat platable surfaces of a disc to provide means for depositing a metallic filmhaving a uniform thickness and magnetic properties. In addition, means are provided for continuously passing a uniform volume of clean electrolyte solution over the platable surfaces of the disc to prevent roughness of the metallic deposit on the platable surfaces and to provide the necessary relative agitation between the electrolytic solution and the disc when connected as a cathode in the electroplating apparatus.

The novel electroplating method of the present invention, both in its basic and preferred forms, utilizes the general principle that to deposit a metallic film of uniform thickness on a flat platable surface a uniform electric field must be generated normal to the platable surface. To accomplish this, in the method of the present invention the member to be plated is immersed in an electrolyte bath containing ions of the metal to be plated such that the flat platable surface of the member is surrounded by and forms an integral portion of a larger, flat, substantially continuous, platable surface. Relative movement may be imparted between the member to be plated and the electrolyte bath preferably by passing clean electrolyte solution over a portion of the larger platable surface including the fiat platable surface of the member to be plated. A uniform electric field is then generated through the electrolyte bath substantially normal to the larger platable surface.

By including the platable surface of the member to be plated within a larger platable surface, the electric field may be nonuniform over outer portions of the larger platable surface while uniform over the entire platable surface of the member to be plated. Thus, the method of the present invention represents a substantial improvement over presently existing electroplating methods and may be practiced with apparatus employing closely spaced electrodes for generating the electric field without requiring auxiliary apparatus to produce a substantially uniform field over the entire surface to be plated as is common in conventional electroplating processes.

Although the method of the present invention may be prac ticed utilizing many different apparatus it is practiced with the apparatus of the preferred form of the present invention by positioning the disc 36 within the opening 42 of the holder member 38 and securing the disc therein by screwing the ring members 48 and 50 about the opening 42. The plug element 56 is positioned within the central opening 54 in the disc 36 and secured therein by screwing the ring members 58 and 60 to the outer surface of the plug member 56 within the opening 54. The holder member 38 thus supporting the disc 36 is positioned within the tank 10 as illustrated in FIGS. 1 and 2. The diaphragm members 68 and 70 and the electrode assemblies 76 and 106 are inserted within the tank as illustrated. Electrolyte solution is then passed through the tube 136 into the baffle box 132. Electrolyte solution passes through the opening 22 in the base of the tank 10 and upward on either side of the holder member 38 between the holder member and the diaphragm members 68 and 70. The electrolytic solution passes through the diaphragm members and over the tops thereof filling the region ofthe tank 10 about the electrode assemblies 76 and 106. Excess electrolytic solution flows from the tank 10 through the port 24 and 26. Equal electric cur rents are then applied to the electrode assemblies 76 and 106 to develop the desired uniform electric field through the electrolyte solution normal to the opposing platable surfaces of the holder member 38 and produce an electroplating of the metallic film on the disc 36 having a uniform thickness and magnetic properties.

Discs of different thicknesses and diameters need to be plated. FIGS. 5-8 show an alternate and preferred embodiment of the holder for holding the member to be electroplated. The holder is constructed with an opening for the largest diameter disc to be plated and for the thickest disc to be plated. An adapter is provided to reduce the larger diameter opening and larger thickness of the holder to that of the smaller dimensioned disc.

FIG. 6 schematically shows the holder 247, which includes the adapter 250. and shows the disc 248 with a plug 274. FIG. 7 shows an enlarged view of the adapter having the disc 248 and plug 274 mounted therein. FIG. 8 shows an enlarged detailed cross-sectional view of the adapter 250 taken along the line 8-8 and shows portions of the disc and outer portion of the holder 247. The outer portion of the holder 247 is similar to holder 34 of FIG. 1 and includes an outer rectangular portion 252 having an opening of a first diameter d and having a thickness a. A disc having an outer diameter substantially the same as that of the opening 254 (i.e., d) and a thickness substantially the same as that of the holder 247 (i.e., a) can be fastened into the opening 254 using thin rings in substantially the same manner as that described with reference to FIG. I. When used in this fashion the use and operation is the same as that described with reference to FIG. 1.

However, it is also desirable to use the same holder to plate a disc 248 having a smaller diameter e and having a smaller thickness 12. To accommodate the smaller diameter and thickness of disc 248, an adapter 250 is provided to adapt the smaller diameter and thickness of disc 248 to the larger diameter opening and thickness of holder 247. The result is a substantially continuous platable surface across the entire cross section of the holder which, in turn, covers substantially the entire cross section ofelectrolyte solution in the tank 10 of FIG. 1. To this end, the outside dimensions are such that the holder 247 extends essentially from side to side in the tank and from at least the top of the electrolyte to the effective bottom of the tank.

Consider now the details of the adapter 250. The adapter 250 has an inner portion 256 which is a ring-shaped member having an inside diameter slightly larger than the outside diameter of disc 248. The thickness c of the inner portion 256 is substantially the same as the thickness of the disc. Although not essential to the invention, the outside diameter of the inner portion or ring 256 is slightly smaller than the diameter of the opening 254.

A pair of rings 258 and 260, of the same diameter, electrically and mechanically connect the disc 248 to the inner portion 256 of the adapter 250. Bolt and nut assemblies 262 lock the rings together.

The adapter has an outer portion 266 of substantially the same thickness as the outer portion 252 of the holder and the surfaces of each lie in substantially the same plane. The inner portion 256 and the disc are substantially the same thickness and their surfaces lie in substantially the same plane. An inclined surface 268, which is at an oblique angle to the surface of the outer portion 266 and to the surface of the inner portion 256, makes the transition between the thickness 11 and the thickness 0. The inclined surface 268 and outer portion 266 are actually constructed of a pair of ring-shaped members and are fastened together to the inner ring portion 256 by bolts 270 threaded into one of the pair of ring-shaped members.

A nonconductive epoxy material 272, which is resistant to the chemical solutions used during the electroplating process. is filled in cracks and depressions to prevent chemical buildup or leakage between parts. Thus, a ring of epoxy 272 is placed at thejunction of the inclined surface 268 and the inner ring shaped portion 256, at the ends of the bolts 270 and in between the ends of the pair of ring-shaped members making up the outer portion 266.

A pair of rings 274 and 276 and bolts similar to rings 258 and 260 and bolts 262 are used to mechanically and electrically interconnect the outer ring portion 266 to the outer portion 252 of the holder 247.

A plug 274, of substantially the same diameter as the inner opening 275 of the disc 248, fills in the center opening of the disc and a pair of rings electrically and mechanically connect the disc 248 and plug 274 together. Only one ring 276 of the pair can be seen and is shown in FIG. 8. Nut and bolt assemblies 278 mechanically hold the rings 276, plug 274 and disc 248 together. Preferably, all of the exposed parts of the holder 247 (which include the adapter 250) plug 274 and holding rings are made of the same conductive and electroplatable metallic material as the disc 248 to be plated. Thus, the holder, including its adapter 250, the disc 248, the plug 274 and the rings for holding these parts together effectively comprise part of a larger platable surface. Although only one side of the adapter 250, disc 248 and plug 274 has been described. the opposite side is virtually identical and also forms part of a larger platable surface. The larger platable surfaces are actually electrodes and extend from side to side in the tank and from at least the top of the electrolyte solution to the bottom. Stating it differently the larger platable surfaces or electrodes extend over substantially all of the cross section of electrolyte solution. The anode electrodes on either side of the holder 247 also extend across substantially all of the cross section of electrolyte solution. The rectangular configuration of the container or tank 10 effectively contains the electrolyte solution in substantially a right cylindrical volume in between the holder position (cathode) and each anode position. A right cylindrical volume is defined herein as a volume of uniform cross section generated by a straight line moving round a closed curve and remaining parallel to a fixed straight line. The axis of the right cylindrical volume is at a right angle to the anode electrodes and to each flat surface of the disc being plated. As a result, substantially continuous platable surfaces extend over substantially all of the cross section of electrolyte solution enabling a magnetic recording film of uniform thickness to be electroplated as explained in connection with FIG. 1.

The change in thickness between the outer portions 252 and 266 and the inner portion 256 causes a difference in planes of the platable surfaces. However, the distance between the plane of the outer portions 252 and 266 and that of the inner portion 256 and disc 248 is small and effectively negligible compared to the distance between anode and cathode elec- I trodes. Also, as can be seen in FIG. 7, the point of the transition between planes or thickness is separated by a relatively large distance by the inner ring portion 256. Thus, the effect of the change in planes or thickness has negligible effect on the electrical field in the electrolyte solution near the surfaces of the disc 248 to be plated. The gradual incline of the platable surface 268 further reduces the distortion of the field caused by the transition.

It will also be noted that the epoxy ring 272 at the transition between the inclined surface 268 and the inner ring portion 256 causes a discontinuity in the platable surface. However, due to its distance from the disc being plated and the narrow width of the ring of epoxy, it has negligible effect on the electrical field in the electrolyte in the area of the disc and hence negligible effect on the thickness of the magnetic material being plated. Effectively a substantially continuous platable surface is provided by the holder and disc and plug over the cross section of solution.

It should also be noted that the various pairs of rings holding the plug, the disc and the adapter in place in the holder are quite thin and hence have very little effect on the electrical field in the electrolyte over essentially all of the disc being plated. Any decrease in thickness of the plating caused by the rings can be easily compensated for by putting a small ring of epoxy about the edge of the pair of rings next to the area where the decrease in thickness would occur, such as at the inner edge of rings 260 and 258.

The holder of FIG. 1 or FIGS. 7 and 8 can be made large enough to provide two or more openings and mount two or more discs therein. The additional disc or discs close in the holder providing a substantially continuous electrode surface and can be considered part of the holder when speaking of another disc in the holder.

FIGS. 9 and 10 depict, schematically, a plating apparatus coming within the broader teachings of the present invention. Depicted is a container 202 similar to container 10 of FIG. 1 having sides 204 and 206, ends 208 and 210, and a bottom 212. The sides, ends and walls are all made of a nonconductive material or are coated with a nonconductor so as to have a nonconductive surface 214. Thus, the container 202 together with gravity acting on top of the electrolyte solution, as is true of tank 10 of FIG. 1, provides a right cylindrical volume for containing an electrolyte solution 217 in between electrodes 218 and 222. Although not shown, an opening may be provided in the bottom of the tank at holder 220 for receiving filtered electrolyte from a baffle box or the like as described in connection with FIG. 1.

The electrodes 218 and 222 are anode electrodes and are the same as the anode electrodes of FIG. 1 extending over substantially all of the cross section for containing solution provided by the inside surface 214 of the container 202. However, in contrast to the previous figures, the cathode electrode has a holder 220 without an opening for the member to be plated. Instead, a member to be plated is attached on each face of the holder 220. The members to be plated are again thin disc-shaped members 228 and 230 and are attached on the surface of the holder 220 by means of a fastener 232, such as a nut and bolt.

The holder 220 is metallic and has a platable surface on each face that extends from side 204 to side 206 and from the top of the electrolyte 217 to the bottom 212. The member to be plated (228 or 230) is completely immersed in the electrolyte 217. In this manner, the holder 220 not only holds the member to be plated, but the conductive surface thereof together with the surface of the member to be electroplated comprise a larger platable surface extending across the entire cross section of electrolyte. The thickness of the discs 228 and 230 is very small compared with the distance between the electrodes 218 and 222 and the members 228 and 230, respectively. As a result, a magnetic recording film may be electrodeposited on the discs 228 and 230 which is highly uniform over substantially the entire surface.

Although it is felt that the embodiment of FIGS. 9 and 10 come within the broader concepts of the invention, the embodiments of the invention wherein the member to be plated is placed in an opening is a preferred embodiment, having nu merous advantages over the embodiment of FIGS. 9 and 10. For example, the embodiment employing the platable member in an opening of a holder allows two opposing surfaces of the same member to be plated at the same time. Also, a uniform thickness is obtained over essentially all of both platable sur' faces of the member, whereas in the embodiment of FIGS. 10 and 11 only one of two opposing platable surfaces of the same member (being plated) can be plated at one time. Additionally, a variation in thickness of the electroplated film on the member being plated in accordance with the teachings of FIGS. 9 and 10 will be found approaching the edges of the platable surface of the member due to the step change in thickness from the member to the holder, especially for thicker members.

FIGS. 11 and 12 show another embodiment of the holder within the broader concepts of the invention. Here a discshaped master 236 for a phonograph record stamper is inserted in an opening of a holder 237. The opening is defined by a nonconductive ring 238 which surrounds the master 236. Surrounding the ring 238 is a rectangular-shaped sheet of metal 240 which is fastened (by means not shown) to. and makes electrical contact with, a conductive backing 242. The master 236 can be closely fitted into the nonconductive ring so as to hold it in place or the master can be fastened in place by nut and bolt 244.

The master 236 is typically a nonconductive material with a thin conductive or platable film 235, The nut and bolt assembly 244 makes an electrical contact between the conductive backing 242 and the surface 235.

The holder 237 including 242 and 240 and master 236 is immersed with the member to be plated in a container such as that shown schematically in FIGS. 9 and 10. However, only one anode electrode is needed as the back side of the holder need not be plated. The holder 237 and the master 236 are connected as a cathode electrode and the platable surfaces of the holder 237 and the master 236 are electroplated. The conductive surface of the metal sheet 240 is dimensioned so that it extends the platable surface of the member 236 from side to side in the container and from the top to bottom of the electrolyte solution in the container. Thus, with the master 236 and the sheet 240 forms part of a larger platable surface which extends a substantially continuous conductive platable surface across substantially all of the cross section of electrolyte solution.

The nonconductive ring is very thin and extends slightly above the surfaces of 236 and 240 and provides a small discontinuity between the platable surfaces of the sheet 240 and the master 236 to prevent the electroplated surface from bridging the gap between the master 236 and the sheet 240 during electroplating.

As an alternative to the conductive backing member 242, the backing member 242 could be replaced by a nonconductive member and some means provided to make an electrical connection between the conductive member 240 and the conductive surface 235 ofthe master 236.

FIG. 13 shows a preferred control system for applying electrical current between electrodes for electroplating in a system such as that shown in FIGS. 1 and 9 where two opposing surfaces are to be electroplated at the same time.

The holder and member to be plated form a cathode electrode C and the electrodes at each side of the holder form the anode electrodes A.

Independently controllable rectifier circuits 290 and 292 provide current between electrodes. The negative outputs of the rectifier circuits 290 and 292 are connected together to the cathode, whereas the positive output of rectifier circuits 290 and 292 are separately connected to different ones of the anodes.

Current sensing circuits 298 and 300 sense current flow through different ones of the anodes. The sensing circuits are conventional current shunts using a resistor in series with the anode with the voltage across the resistor used as the output.

Control circuits 294 and 296 sense the current from the sensing circuits 298 and 300 and apply a control signal, corresponding to the amount of current sensed, to the controllable rectifier circuits 290 and 292, respectively. With this arrangement, the controllable rectifier circuits can be adjusted to provide the same or different amounts of current through their respective anodes. The control circuits 290 and 292 then maintain constant currents through their corresponding anodes under control of the control signals from respective control circuits 294 and 296. As a result, the anode electrodes need not be equally spaced from the cathode and, should the resistance in one anode circuit be different from the other, the same current can be forced through each. Another advantage of this arrangement is that a different current can be applied through one anode circuit than the other and, as a result, a different thickness of electroplate can be plated on opposing surfaces of the same or different members being plated. Also, by turning one rectifier off, only one side can be plated.

The control circuits 294 are conventional current integrator and control circuits for rectifier circuits and each of circuits 290-300 are well known in the electroplating art.

lelaim:

1. Apparatus for electrodepositing a uniform metallic film on a platable surface ofa member to be plated, comprising:

a tank having inner walls of a nonconductive material and being adapted for containing an electrolyte solution; holder means having a platable surface and an opening therein for receiving the member to be plated;

means for supporting the member to be plated in the opening such that the platable surface of the member forms a substantially continuous surface with the platable surface of the holder;

an electrode assembly having an electrode surface which is similar to the continuous surface;

a porous diaphragm member of nonconductive material which is insoluble in the electrolyte solution for passing the solution through its pores only when a predetermined pressure differential is developed thereacross;

means for mounting the holder means in the tank;

means for mounting the electrode assembly in the tank such that the electrode surface and the continuous surface form similar surfaces;

means for mounting the diaphragm member to extend from the bottom of the tank upward adjacent the continuous surface and between the holder means and the electrode assembly;

means for directing clean electrolyte solution upward between the holder means and the diaphragm over the continuous surface to develop a pressure differential across the diaphragm member which prevents flow of electrolyte solution through the diaphragm member towards the holder means;

and means for developing a uniform electric field through the electrolyte solution and diaphragm member between the electrode assembly and the holder means substantially normal to the continuous surface.

2. Apparatus for electrodepositing a uniform metallic film on a substantially flat platable surface of a member to be plated, comprising:

means forming a pair of substantially parallel walls having opposing surfaces ofa nonconductive material;

holder means having a substantially flat platable surface and an opening therein for receiving the member to be plated;

means for supporting the member to be plated in the opening such that the platable surface of the member forms a substantially flat surface with the platable surface of the holder means;

an electrode assembly having a substantially flat electrode surface;

a porous diaphragm member of nonconductive material which is insoluble in electrolyte solutions for passing an electrolyte solution through its pores when a predetermined pressure differential is developed thereacross;

means for vertically mounting the holder means to extend a flat platable surface between and substantially normal to the parallel walls;

means for vertically mounting the electrode assembly to extend a flat electrode surface between the parallel walls substantially parallel to the platable surface of the holder means;

means for vertically mounting the diaphragm member to ex tend upward and between the parallel walls adjacent the holder means;

means for directing an electrolyte solution containing ions of the metal to be electrodeposited to flow upward between the holder means and the diaphragm member over the platable surfaces of the holder means and the member to be plated and into a region between the diaphragm member and the electrode assembly at a height at which a pressure differential is developed across the diaphragm member sufficient to prevent the flow of electrolyte solution through the diaphragm member towards the holder means;

and means for electrically connecting the electrode assembly as an anode and the holder means as a cathode in cluding means for applying a current signal to the electrode assembly to develop a parallel electric field between the flat surfaces of the holder means and the electrode assembly normal to the platable surface of the member to be plated.

3. The apparatus defined in claim 2 wherein the means forming the parallel walls is a tank including a fluid discharge means having an opening adjacent the electrode assembly, the height of the opening being slightly less than the height at which the electrolyte solution passes into the region between the diaphragm member and the electrode assembly.

4. The apparatus defined in claim 3 wherein the means for directing the electrolyte solution upward between the holder means and the diaphragm member includes a slot in the bottom of the tank adjacent the holder means as mounted in the tank and extending between the parallel walls and means for introducing solution along the slot at a uniform pressure to flow upward between the holder means and the diaphragm member.

5. Apparatus for simultaneously electrodepositing uniform metallic films on opposing substantially flat platable surfaces ofa member to be plated, comprising:

a tank having a bottom and normal thereto two opposing substantially parallel, inner walls all of a nonconductive material, the tank being adapted for containing an electrolyte solution;

holder means having opposing substantially flat platable surfaces and an opening therein of substantially the same shape as the member to be plated;

means for supporting the member to be plated in the opening such that the opposing platable surfaces of the member form substantially flat continuous surfaces with the opposing platable surfaces of the holder means;

first and second electrode assemblies having substantially flat electrode surfaces;

means mounting the holder means in the tank substantially normal to the'opposing walls to divide the tank into first and second compartments;

means mounting the first electrode assembly in the first compartment to extend a flat electrode surface between the opposing walls substantially parallel to a flat platable surface of the member to be plated;

means mounting the second electrode assembly in the second compartment to extend a flat electrode surface between the opposing walls substantially parallel to an opposing flat platable surface ofthe member to be plated;

the flat platable surfaces and the flat electrode surfaces each extending essentially up to and normal to the bottom and the two walls of the tank;

and means for developing a uniform parallel electric field between the first and second electrode assemblies and the holder means through the electrolyte solution contained in the first and second compartments substantially normal to the opposing flat platable surfaces of the member to be plated.

6. Apparatus for simultaneously electrodepositing uniform metallic films on opposing substantially flat platable surfaces of a member to be plated, comprising:

a tank having inner walls of a nonconductive material, two of the walls being opposite and substantially parallel to each other, the tank being adapted for containing an electrolyte solution;

holder means having opposing substantially flat platable surfaces and an opening therein for receiving the member to be plated;

means for supporting the member to be plated in the opening such that the opposing platable surfaces of the member form substantially flat surfaces with the opposing platable surface of the holder;

first and second electrode assemblies, each having a substantially flat electrode surface;

first and second porous diaphragm members of a nonconductive material which is insoluble in the electrolyte solution for passing the electrolyte solution through its pores when a predetermined pressure differential is developed thereacross;

means for mounting the holder means to extend opposing flat platable surfaces between and substantially normal to the opposite walls of the tank to divide the tank into first and second separate compartments;

means for mounting the first electrode assembly in the first compartment to extend a flat electrode surface between the opposite walls of the tank substantially parallel to one of the flat platable surfaces of the member to be plated;

means for mounting the second electrode assembly in the second compartment to extend a flat electrode surface between the opposite walls of the tank substantially parallel to the remaining flat platable surface of the member to be plated;

means for mounting the first diaphragm member in the first compartment to extend upward from the bottom of the tank and between the opposite walls of the tank adjacent to the holder means to isolate the holder means from the solution adjacent the first electrode assembly;

means for mounting the second diaphragm member in the second compartment to extend upward from the bottom of the tank and between the opposite walls of the tank adjacent the holder means to isolate the holder means from the solution adjacent the second electrode assembly;

means for causing clean electrolytic solution to flow from the bottom of the tank upward between the holder means and the first and second diaphragm members to pass fresh electrolyte solution over the opposing plating surfaces of the holder means and the member to be plated and into regions between the diaphragm members and the first and second electrode assemblies, respectively, at heights at which a pressure differential is developed across the first and second diaphragm members sufficient to prevent flow of the electrolyte solution through the diaphragm members toward the holder means;

and means for electrically connecting the first and second electrode assemblies as anodes and the holder means as a cathode including means for applying a current signal to the first and second electrode assemblies to develop uniform, parallel electric fields between the flat surfaces of the holder and the first and second electrode assemblies normal to the opposing platable surfaces of the member to be plated.

7. The apparatus defined in claim 6 including first and second fluid discharge means having openings adjacent the first and second electrode assemblies, respectively, the heights of the openings being slightly less than the heights at which the electrolyte solution passes into the regions between the first and second diaphragm members and the first and second electrode assemblies.

8. Apparatus for use in the electrodepositing of metallic films on members having substantially flat opposing platable surfaces, comprising:

a holder having opposing substantially flat platable surfaces and an opening therein for receiving the member to be plated;

means for supporting the member to be plated in the opening such that the opposing platable surfaces of the member form substantially flat surfaces with the opposing platable surfaces of the holder;

first and second electrode assemblies each having a substantially flat electrode surface;

first and second porous diaphragm members of nonconductive material for passing an electrolyte solution through its pores only when a predetermined pressure differential is developed thereacross;

and a tank having two opposing inner walls of nonconductive material, which are substantially parallel to each other and including means defining a slot in the bottom of the tank, means for receiving the holder with the member to be plated to extend the flat platable surfaces between and substantially normal to the opposing walls over the slot to divide the tank into two compartments, means adjacent and on opposite sides of the holder as mounted in the tank for receiving the first and second diaphragm members, respectively, to extend from the bottom of the tank upward to a predetermined height and between the opposite walls of the tank, means positioned on opposite sides of the holder as mounted in the tank and spaced from the means for receiving the first and second diaphragm members for receiving the first and second electrode assemblies, respectively, such that the flat electrode surfaces thereof are substantially parallel to the opposing platable surfaces of the holder, and first and second fluid discharge means having openings adjacent the first and second electrode assemblies, respectively, as mounted in the tank, the height of the openings being slightly less than the predetermined height of the first and second diaphragm members as mounted in the tank.

9. The apparatus defined in claim 8 including means for introducing fluid along the slot in the bottom of the tank at a uniform pressure to rise upward on opposite sides of the holder between the holder and the first and second diaphragm members.

10. The apparatus defined in claim 9 wherein the means for introducing fluid at a uniform pressure includes a tapered tube having its smaller end enclosed and its larger end positioned to receive the fluid, the tapered tube having ports therein spaced from each other and facing the slot in the bottom of the tank, and a baffle for smoothing the flow of fluid through the ports positioned between the slot in the bottom of the tank and the ports in the tapered tube.

11. Apparatus for electroplating a uniform metallic film on a substantially flat platable surface of a member to be plated, comprising:

a container for an electrolyte solution having an interior nonconductive surface defining a predetermined cross section for containing an electrolyte solution,

a holder having a flat platable surface and an opening therein for receiving the member such that the flat surface of the member forms a continuous surface with the flat surface of the holder, the continuous surface being mounted in the container at a right angle to said nonconductive surface and extending over essentially all of said predetermined cross section.

12. Apparatus according to claim 11 including means for generating an electric field through the electrolyte solution, the shape of the container and the generating means applying a uniform electric field up to and normal to substantially all of the continuous surface extending across the cross section of solution.

13. Apparatus as defined in claim 11 including means for securing the member to be plated within the opening in said holder.

ble surfaces, the member to be plated being mountable in the opening of said holder such that the opposing flat surfaces of the member form opposing continuous surfaces with the flat surfaces of the holder, the generating means generating said field to both of the opposing continuous surfaces.

16. Apparatus as defined in claim comprising means for passing clean electrolyte solution over at least a portion of both of the continuous surfaces including the flat platable surfaces of the member.

17. Apparatus for electroplating a uniform metallic film on a substantially flat platable surface of a member to be plated, comprising:

a container for an electrolyte solution having an interior surface for containing an electrolyte solution, spacedapart positions existing along said interior surface for an electrode and a member to be plated, the interior nonconductive surface defining a substantially constant cross section in size and shape in between the electrode position and the member position for containing the electrolyte solution,

an electrode having a flat surface,

a holder having a flat platable surface and an opening therein for receiving the member to be plated such that the flat surface of the member forms a continuous surface with the flat surface of the holder, the continuous surface of said holder and the flat surface of said electrode being parallel to each other and mounted at the electrode and member positions, respectively, at right angles to said nonconductive surface and extending over essentially all of said cross section at the respective positions.

18. Apparatus according to claim 17 wherein the said interior surface comprises two flat parallel sidewalls and a flat bottom normal to said sidewalls,

19. Apparatus for electroplating a uniform metallic film on a substantially flat platable surface of a member to be plated, comprising:

a container for an electrolyte solution having at least two parallel interior nonconductive sidewalls and a nonconductive bottom for containing the solution;

an electrode having a flat surface;

a holder having a flat platable surface and an opening therein for receiving the member to be plated such that the flat surface of the member forms a continuous surface with the flat surface ofthe holder;

the continuous surface of said holder and the flat surface of said electrode being spaced apart parallel to each other and mounted in said container at right angles to said walls and bottom and extending essentially from wall to wall and to the bottom such that the platable surface of the member may be completely immersed in the solution.

20. Apparatus according to claim 19 wherein said walls and bottom are arranged such that said flat electrode surface and said flat continuous surface covering said cross section are positioned in direct alignment.

21. Apparatus for electroplating a uniform metallic film on a substantially flat platable surface of a member to be plated, comprising:

a container for an electrolyte solution having a nonconductive interior surface defining a predetermined rectangular cross section, in between an electrode position and a position for the member to be plated for confining an electrolyte solution;

an electrode having a flat surface;

a holder having a flat platable surface and an opening therein for receiving the member such that the flat surface of said member forms a continuous surface with the flat surface ofsaid holder;

said electrodes and holder being mounted in the interior of said container at the respective electrode and member positions parallel to each other and normal to said interior surface and both extending essentially from side to side and to the bottom of said rectangular cross section to thereby permit a uniform electric field to be generated in the solution over at least a portion of said continuous flat surface including the platable surface of the member.

22. A member having a metallic film of uniform thickness and magnetic properties electrodeposited on a flat platable surface thereof in a fluid electrolyte solution contained so as to have a predetermined cross section in size and shape while the member is mounted in a holder having a flat platable surface continuous with and surrounding the flat platable surface of the member, the flat continuous surface extending over the cross section of fluid while a uniform electric field is generated through the electrolyte of predetermined cross section up to the continuous surface.

23. Apparatus for electrodepositing a uniform metallic film on a substantially flat platable surface of a member to be plated, comprising:

a tank having two opposing inner walls and a bottom wall of a nonconductive material adapted for containing an electrolyte solution;

holder means having a substantially flat platable surface and an opening therein for receiving the member to be plated;

means for supporting the member to be plated in the opening such that the platable surface of the member forms a substantially flat continuous surface with the platable surface of the holder;

an electrode assembly having a substantially flat electrode surface;

means mounting the holder means within the tank, the

holder means extending a flat platable surface substantially normal to the opposing walls of the tank extending essentially from one of said walls to the other and to said bottom wall such that the platable surface of the member to be plated may be completely immersed in the electrolyte solution; and

means mounting the electrode assembly within the tank, the electrode assembly extending a flat electrode surface from essentially one of said opposing walls of the tank to essentially the other and to the bottom wall and substantially parallel to the platable surface of the holder means.

24. Apparatus as defined in claim 23 including means for electrically connecting the electrode assembly as an anode and the holder means and the member to be plated as a cathode including means for applying a current signal to the electrode assembly, the shape of the tank permitting a uniform parallel electric field to be formed between and substantially normal to the flat surfaces of the holder means and the electrode assembly.

25. The apparatus defined in claim 23 including means for imparting relative movement between the holder and the electrolyte solution adjacent thereto.

26. Apparatus for electrodepositing a uniform metallic film on a platable surface of a member to be plated comprising:

a tank having two parallel sides and normal thereto a bottom which are formed of an electrically nonconductive material and being adapted for containing an electrolyte solution;

rectangular-shaped holder means having a platable surface and an opening therein for receiving the member to be plated;

means for supporting the member to be plated in the opening such that the platable surface of the member forms a substantially continuous surface with the platable surface of the holder means;

a rectangular-shaped electrode assembly having an electrode surface;

means mounting the holder means in the tank normal to both sides and to the bottom;

means mounting the electrode assembly in the tank normal to both sides and to the bottom;

the electrode assembly and holder means being constructed such that the electrode surface and continuous surface extend essentially from one of the sides to the other and to the bottom of the tank.

27. Apparatus as defined in claim 26 including means for developing an electric signal between the electrode assembly and the holder means thereby forming a uniform field substantially normal to the continuous surface.

28. Apparatus defined in claim 26 including means for imparting relative movement between the holder means and the electrolyte solution adjacent thereto.

29. Apparatus for electrodepositing a uniform metallic film on a substantially flat platable surface of a member to be plated, comprising:

container means forming a bottom and normal thereto a pair of substantially parallel walls having opposing surfaces all of a nonconductive material;

holder means having a pair of substantially flat platable surfaces and an opening therein for receiving the member to be plated;

means for supporting the member to be plated in the opening such that the platable surfaces of the member forms substantially flat continuous surfaces with the platable surfaces of the holder;

a pair of electrode assemblies each having a substantially flat electrode surface;

means mounting the holder means normal to the parallel walls and to the bottom, the outer periphery of the platable surfaces extending essentially up to and following the contour of the parallel walls and the bottom; and

means mounting the electrode assemblies on either side of the holder means normal to the parallel walls and the bottom, the outer periphery of the electrode surfaces extending essentially up to and following the contour of the parallel walls and the bottom,

30. Apparatus according to claim 29 including means for developing an electric field between the electrode assemblies and the holder means thereby forming a uniform field normal to the continuous surfaces.

31. Apparatus according to claim 29 including means for directing clean electrolytic solution over the flat surface of the holder means between the holder means and the electrode assembly, the electrolyte solution containing ions of the metal to be electrodeposited, the electrolytic solution in the container means passing over the member to be plated.

32. Apparatus for electroplating a uniform metallic film on a substantially flat platable surface of a member to be plated having an outer periphery of a first size and shape, comprising:

a container for an electrolyte solution having an interior nonconductive surface defining a predetermined interior cross section having an outer periphery of a second size and shape for containing an electrolyte solution,

a holder having a flat platable surface and an opening therein of substantially the same size and shape as the outer periphery of said member, the flat surface of the member forming a continuous surface with the flat surface of the holder, when mounted in said opening, the continuous surface of said holder being mounted in the container at a right angle to said nonconductive surface and extending over essentially all of said predetermined cross section to permit a uniform electric field to be applied in the solution up to and normal to substantially all of the continuous surface in the solution.

33. Apparatus for electroplating a uniform metallic film on a substantially flat platable surface of a member to be plated having an outer periphery of a first size and shape, comprising:

a container for an electrolyte solution having an interior nonconductive surface defining a predetermined interior cross section having an outer periphery of a second size and shape for containing an electrolyte solution,

a holder having a flat platable surface and an opening therein of substantially the same size and shape as the outer periphery of said member, the flat surface of the member forming a continuous surface with the flat surface of the holder, when mounted in said opening, the continuous surface of said holder being mounted in the container at a right angle to said nonconductive surface and extending over essentially all of said predetermined cross section, and

means for generating an electric field through the elec trolyte solution, the shape of the container and the generating means causing a unifoml electric field to be applied in the solution up to and normal to substantially all of the continuous surface in the solution.

34. Apparatus for electroplating a uniform metallic film on a substantially flat platable surface of a member to be plated, the member having an outer periphery of a first size and shape, the apparatus comprising:

a tank including two sides and a bottom having a cross-sectional shape or size different from that of the outer periphery of the member to be plated, the tank being adapted for containing an electrolyte solution;

holder means having a flat platable surface and an opening therein of substantially the same size and shape as the member to be plated, the holder means having an outer periphery of substantially the same shape as the cross-sectional shape of the sides and bottom of the tank and dimensioned to extend essentially from side to side and to the bottom of the tank;

means for supporting the member to be plated in the opening such that the platable surface of the member forms a substantially continuous surface with the platable surface of the holder means;

an electrode assembly having a substantially flat electrode surface and an outer periphery of substantially the same shape as the cross-sectional shape of the sides and bottom of the tank and extending essentially from side to side and to the bottom of the tank;

means supporting the holder means and electrode assembly spaced apart and parallel to each other in said tank and substantially normal to the sides and to the bottom of said tank.

35. Apparatus according to claim 34 including means for electrically connecting the electrode assembly as an anode and the member to be plated and the holder means as a cathode, the shape of the sides and bottom permitting a uniform electric field to be formed over substantially all of the continuous surface.

36. A process for electroplating a metallic film of uniform thickness on a flat platable surface of a member to be plated, comprising the steps of:

positioning the member to be plated in a holder such that the flat platable surface is surrounded by and forms an integral portion of a larger flat, substantially continuous, platable surface with the holder;

immersing the flat platable surface in an electrolyte solution which is contained within a predetermined cross section such that the larger flat platable surface extends over essentially all of said cross section of solution; and

generating a uniform electric field through the electrolyte solution up to and normal to substantially all of said larger flat continuous platable surface which is extending over said cross section of solution.

37. A process as defined in claim 36 wherein the step of generating includes the step of positioning an electrode in the contained solution which extends over essentially all of said cross section of solution.

38. A process as defined in claim 37 wherein the electrode and larger flat continuous platable surface are aligned parallel with respect to each other.

39. A process as defined in claim 38 wherein the solution is contained within substantially the same cross section in between said electrode and said larger flat continuous platable surface.

40. A process for electroplating a metallic film of uniform thickness on a flat platable surface of a member to be plated, comprising the steps of:

positioning the member to be plated in an opening in a holder having a substantially flat rectangular platable surface such that the flat platable surface of the member is surrounded by and forms an integral portion of a larger flat, substantially continuous, platable surface with the holder;

containing an electrolyte solution within a rectangular cross section of substantially the same size and shape as said larger flat rectangular platable surface;

immersing said continuous platable surface in said contained solution extending the larger flat continuous platable surface over essentially all of said cross section of solution; and

generating a uniform electric field through the electrolyte solution up to and normal to substantially all of said larger flat continuous platable surface which is extending over said cross section of solution.

41. A process for simultaneously electroplating metallic films of uniform thickness on opposing flat platable surfaces of a member to be plated, comprising the steps of:

positioning the member within a holder having opposing flat platable surfaces such that the flat opposing surfaces of the member form part of larger continuous flat surfaces with the opposing surfaces of the holder;

immersing the flat platable surfaces in an electrolyte solution which is contained within a predetermined cross section such that the larger flat platable surfaces extend over essentially all of said cross section of solution; and

generating a uniform electric field through the electrolyte solution up to and normal to substantially all of said larger flat continuous platable surfaces which are extending over said cross section of solution.

42. A process as defined in claim 41 wherein the step of generating includes the step of positioning electrodes in said solution on opposite sides of said holder both electrodes extending surfaces over essentially all of said cross section of solution.

43. A process as defined in claim 42 wherein the electrodes and larger flat continuous platable surfaces are aligned parallel with respect to each other.

44. A process as defined in claim 42 wherein the solution is contained within substantially the same cross section in between said electrodes and said larger flat continuous plata ble surfaces.

45. Apparatus for electroplating a uniform metallic film on a substantially flat platable surface of a member, comprising:

a container having an interior nonconductive surface for containing an electrolyte solution in a substantially right cylindrical volume in between first and second electrode positions, first and second substantially parallel electrodes respectively positioned at said first and second positions and extending substantially normal to said non conductive surface over substantially all of the cross section of said volume thereby enabling a substantially uniform electric field to be generated throughout the solution between the electrodes, and a platable holder constructed for mounting said member and having a substantially flat electroplatable surface, said electroplatable surfaces of said holder and said member being electrically connected together and comprising part of a larger plata' ble surface comprising said first electrode.

46. Apparatus according to claim 45 wherein said holder has an opening for receiving said member and said flat electroplatable surface is positioned in substantially the same plane as said flat platable surface of said member.

47. Apparatus according to claim 46 wherein said holder comprises a clamping member for bridging said member and holder and extending around said member to be plated.

48. Apparatus according to claim 46 wherein said holder comprises an inner platable surface immediately surrounding said member in substantially the same plane as the platable surface of said member and an outer surface extending around said inner surface in a different plane.

49. Apparatus according to claim 48 wherein said holder comprises a removable adapter which extends around said member and which includes said inner surface.

50. Apparatus according to claim 49 wherein said adapter has a further surface extending around said inner surface in the same plane as said outer surface.

51. Apparatus according to claim 50 including first and second electrically conductive clamping members extending respectively around the outer edges of said member and said further surface of said adapter for electrically and mechanically interconnecting said member to said inner surface and said further surface to said outer surface.

52. Apparatus according to claim 50 wherein said adapter comprises an inclined surface at an oblique angle to said inner and outer surfaces for providing a transition between the different planes.

53. Apparatus according to claim 50 wherein said member and said opening are round and said adapter is ring-shaped.

54. Apparatus according to claim 46 wherein said member has an opening therein and wherein said first electrode additionally comprises an electroplatable member electrically and mechanically connected to said member in the opening thereof.

55. Apparatus according to claim 45 wherein said member has opposing substantially flat parallel platable surfaces and wherein the container contains the electrolyte solution in said right cylindrical volume to a third position on the opposite side of said first position from said second position, a third electrode parallel to said first electrode and extending substantially normal to said nonconductive surface over substantially all of the cross section of said volume.

56. Apparatus according to claim comprising means for applying plating currents between said first and second electrodes and between said first and third electrodes.

57. Apparatus according to claim 56 wherein said means for applying plating currents comprises means for independently regulating the plating currents between said second and first electrodes and between said third and first electrodes.

58. Apparatus according to claim 45 including a narrow nonconductive member interposed between said electroplatable surfaces of said member and of said holder.

59. Apparatus according to claim 58 wherein said nonconductive member extends above at least one of said electroplatable surfaces.

60. Apparatus for electroplating a uniform metallic film on a substantially flat platable surface of a member having a predetermined peripheral configuration, comprising:

a container having an interior nonconductive surface defining a substantially right cylindrical volume for containing an electrolyte solution in between first and second electrode positions, the cross-sectional configuration of said volume being different from the predetermined configuration of said member, first and second substantially parallel electrodes respectively positioned at said first and second positions, said first and second electrodes extending substantially normal to said nonconductive surface across substantially all of the cross section of said volume, said first electrode comprising a holder having a platable surface and having an opening of substantially the same configuration as said predetermined peripheral configuration of said member and adapted for receiving said member, said first electrode having a platable surface comprising the platable surface of said holder extending from around said opening across substantially all of the cross section of said volume enabling a substantially uniform electrical field to be generated throughout the solution between the electrodes when said member is mounted therein.

61. Apparatus according to claim 60 comprising a clamping member for securing said member in the opening of said holder.

62. Apparatus according to claim 60 wherein said holder comprises an inner platable surface immediately surrounding said opening in substantially the same plane as the platable surface of said member when mounted therein and an outer surface around said inner surface positioned in a different plane.

63. Apparatus according to claim 62 wherein said holder comprises a removable adapter which surrounds said opening and which includes said inner surface.

64. Apparatus according to claim 63 wherein said adapter has a further surface around said inner surface in the same plane as said outer surface.

65. Apparatus according to claim 64 including first and second electrically conductive clamping members extending respectively around the outer edges of said opening and said further surface of said adapter for electrically and mechanically interconnecting said member to said inner surface and said further surface to said outer surface.

66. Apparatus according to claim 64 wherein said adapter comprises an inclined platable surface at an oblique angle to said inner and outer surfaces for providing a transition between the surfaces at different planes.

67. Apparatus according to claim 64 wherein the peripheral configuration of said member and said opening are round and said adapter is ring-shaped.

68. Apparatus according to claim 45 wherein said member has opposing substantially flat parallel platable surfaces and wherein the container contains the electrolyte solution in the substantially right cylindrical volume to a third position on the opposite side of said first position from said second position, and a third electrode parallel to said first electrode and extending substantially normal to said nonconductive surface across substantially all of the cross section of said volume.

69. Apparatus according to claim 60 wherein said nonconductive surface comprises two flat and parallel walls and a bottom normal to said sides.

70. A member having a metallic film of uniform thickness and magnetic properties electrodeposited on a flat platable surface thereof in a fluid electrolyte solution contained so as to have a substantially right angle cylindrical volume while the member is mounted on a holder therefor having a platable sur- 71. A process for electroplating a metallic film of uniform thickness on a flat platable surface of a member, comprising the steps of:

positioning the member to be plated in a holder having a platable surface such that the flat platable surface of the member forms a portion of a larger platable surface with the holder; immersing the larger platable surface in an electrolyte solution which is contained within a substantially constant cross section such that the larger platable surface extends over substantially all of said cross section of solution; and generating a uniform electric field through the electrolyte solution up to and normal to substantially all of said larger platable surface.

72. A process as defined in claim 71 comprising the step of positioning an electrode in said electrolyte solution substantially parallel to the larger platable surface and extending substantially continuously over all of said cross section of solution, containing the electrolyte solution in a cylinder having an axis perpendicular to both said electrode and larger platable surface.

73. A process as defined in claim 70 wherein said cross section is substantially rectangular.

74. A process for simultaneously electroplating metallic films of uniform thickness on opposing flat platable surfaces of a member to be plated, comprising the steps of:

positioning the member within a holder having opposing flat platable surfaces such that the flat opposing surfaces of the member form part of larger platable surfaces with the o posing surfaces of the holder; immersing the flat platab e surfaces in an electrolyte solution which IS contained within a substantially constant cross section such that the larger platable surfaces extend over substantially all of said cross section of solution; and generating a uniform electric field through the electrolyte solution up to and normal to substantially all of said larger platable surfaces which are extending over said cross section of solution. 75. A process as defined in claim 74 comprising the step of positioning a pair of electrodes in said electrolyte solution on either side of and substantially parallel to the larger platable face, Said Surfaces of said member and holder forming part of surfaces and extending substantially continuously over all of a larger platable surface extending over substantially all of the cross section of said volume while a uniform electric field is generated through the solution normal to and up to the larger surface.

said cross section of solution, containing the electrolyte solution in a cylinder having an axis perpendicular to both of said electrodes and to said larger platable surfaces. 

2. Apparatus for electrodepositing a uniform metallic film on a substantially flat platable surface of a member to be plated, comprising: means forming a pair of substantially parallel walls having opposing surfaces of a nonconductive material; holder means having a substantially flat platable surface and an opening therein for receiving the member to be plated; means for supporting the member to be plated in the opening such that the platable surface of the member forms a substantially flat surface with the platable surface of the holder means; an electrode assembly having a substantially flat electrode surface; a porous diaphragm member of nonconductive material which is insoluble in electrolyte solutions for passing an electrolyte solution through its pores when a predetermined pressure differential is developed thereacross; means for vertically mounting the holder means to extend a flat platable surface between and substantially normal to the parallel walls; means for vertically mounting the electrode assembly to extend a flat electrode surface between the parallel walls substantially parallel to the platable surface of the holder means; means for vertically mounting the diaphragm member to extend upward and between the parallel walls adjacent the holder means; means for directing an electrolyte solution containing ions of the metal to be electrodeposited to flow upward between the holder means and the diaphragm member over the platable surfaces of the holder means and the member to be plated and into a region between the diaphragm member and the electrode assembly at a height at which a pressure differential is developed across the diaphragm member sufficient to prevent the flow of electrolyte solution through the diaphragm member towards the holder means; and means for electrically connecting the electrode assembly as an anode and the holder means as a cathode including means for applying a current signal to the electrode assembly to develop a parallel electric field between the flat surfaces of the holder means and the electrode assembly normal to the platable surface of the member to be plated.
 3. The apparatus defined in claim 2 wherein the means forming the parallel walls is a tank including a fluid discharge means having an opening adjacent the electrode assembly, the height of the opening being slightly less than the height at which the electrolyte solution passes into the region between the diaphragm member and the electrode assembly.
 4. The apparatus defined in claim 3 wherein the means for directing the electrolyte solution upward between the holder means and the diaphragm member includes a slot in the bottom of the tank adjacent the holder means as mounted in the tank and extending between the parallel walls and means for introducing solution along the slot at a uniform pressure to flow upward between the holder means and the diaphragm member.
 5. Apparatus for simultaneously electrodepositing uniform metallic films on opposing substantially flat platable surfaces of a member to be plated, comprising: a tank having a bottom and normal thereto two opposing substantially parallel, inner walls all of a nonconductive material, the tank being adapted for containing an electrolyte solution; holder means having opposing substantially flat platable surfaces and an opening therein of substantially the same shape as the member to be plated; means for supporting the member to be plated in the opening such that the opposing platable surfaces of the member form substantially flat continuous surfaces with the opposing platable surfaces of the holder means; first and second electrode assemblies having substantially flat eLectrode surfaces; means mounting the holder means in the tank substantially normal to the opposing walls to divide the tank into first and second compartments; means mounting the first electrode assembly in the first compartment to extend a flat electrode surface between the opposing walls substantially parallel to a flat platable surface of the member to be plated; means mounting the second electrode assembly in the second compartment to extend a flat electrode surface between the opposing walls substantially parallel to an opposing flat platable surface of the member to be plated; the flat platable surfaces and the flat electrode surfaces each extending essentially up to and normal to the bottom and the two walls of the tank; and means for developing a uniform parallel electric field between the first and second electrode assemblies and the holder means through the electrolyte solution contained in the first and second compartments substantially normal to the opposing flat platable surfaces of the member to be plated.
 6. Apparatus for simultaneously electrodepositing uniform metallic films on opposing substantially flat platable surfaces of a member to be plated, comprising: a tank having inner walls of a nonconductive material, two of the walls being opposite and substantially parallel to each other, the tank being adapted for containing an electrolyte solution; holder means having opposing substantially flat platable surfaces and an opening therein for receiving the member to be plated; means for supporting the member to be plated in the opening such that the opposing platable surfaces of the member form substantially flat surfaces with the opposing platable surface of the holder; first and second electrode assemblies, each having a substantially flat electrode surface; first and second porous diaphragm members of a nonconductive material which is insoluble in the electrolyte solution for passing the electrolyte solution through its pores when a predetermined pressure differential is developed thereacross; means for mounting the holder means to extend opposing flat platable surfaces between and substantially normal to the opposite walls of the tank to divide the tank into first and second separate compartments; means for mounting the first electrode assembly in the first compartment to extend a flat electrode surface between the opposite walls of the tank substantially parallel to one of the flat platable surfaces of the member to be plated; means for mounting the second electrode assembly in the second compartment to extend a flat electrode surface between the opposite walls of the tank substantially parallel to the remaining flat platable surface of the member to be plated; means for mounting the first diaphragm member in the first compartment to extend upward from the bottom of the tank and between the opposite walls of the tank adjacent to the holder means to isolate the holder means from the solution adjacent the first electrode assembly; means for mounting the second diaphragm member in the second compartment to extend upward from the bottom of the tank and between the opposite walls of the tank adjacent the holder means to isolate the holder means from the solution adjacent the second electrode assembly; means for causing clean electrolytic solution to flow from the bottom of the tank upward between the holder means and the first and second diaphragm members to pass fresh electrolyte solution over the opposing plating surfaces of the holder means and the member to be plated and into regions between the diaphragm members and the first and second electrode assemblies, respectively, at heights at which a pressure differential is developed across the first and second diaphragm members sufficient to prevent flow of the electrolyte solution through the diaphragm members toward the holder means; and means for electrically connecting the first and second electrode assemblies as anodes and the holder means as a cathode including means for applying a current signal to the first and second electrode assemblies to develop uniform, parallel electric fields between the flat surfaces of the holder and the first and second electrode assemblies normal to the opposing platable surfaces of the member to be plated.
 7. The apparatus defined in claim 6 including first and second fluid discharge means having openings adjacent the first and second electrode assemblies, respectively, the heights of the openings being slightly less than the heights at which the electrolyte solution passes into the regions between the first and second diaphragm members and the first and second electrode assemblies.
 8. Apparatus for use in the electrodepositing of metallic films on members having substantially flat opposing platable surfaces, comprising: a holder having opposing substantially flat platable surfaces and an opening therein for receiving the member to be plated; means for supporting the member to be plated in the opening such that the opposing platable surfaces of the member form substantially flat surfaces with the opposing platable surfaces of the holder; first and second electrode assemblies each having a substantially flat electrode surface; first and second porous diaphragm members of nonconductive material for passing an electrolyte solution through its pores only when a predetermined pressure differential is developed thereacross; and a tank having two opposing inner walls of nonconductive material, which are substantially parallel to each other and including means defining a slot in the bottom of the tank, means for receiving the holder with the member to be plated to extend the flat platable surfaces between and substantially normal to the opposing walls over the slot to divide the tank into two compartments, means adjacent and on opposite sides of the holder as mounted in the tank for receiving the first and second diaphragm members, respectively, to extend from the bottom of the tank upward to a predetermined height and between the opposite walls of the tank, means positioned on opposite sides of the holder as mounted in the tank and spaced from the means for receiving the first and second diaphragm members for receiving the first and second electrode assemblies, respectively, such that the flat electrode surfaces thereof are substantially parallel to the opposing platable surfaces of the holder, and first and second fluid discharge means having openings adjacent the first and second electrode assemblies, respectively, as mounted in the tank, the height of the openings being slightly less than the predetermined height of the first and second diaphragm members as mounted in the tank.
 9. The apparatus defined in claim 8 including means for introducing fluid along the slot in the bottom of the tank at a uniform pressure to rise upward on opposite sides of the holder between the holder and the first and second diaphragm members.
 10. The apparatus defined in claim 9 wherein the means for introducing fluid at a uniform pressure includes a tapered tube having its smaller end enclosed and its larger end positioned to receive the fluid, the tapered tube having ports therein spaced from each other and facing the slot in the bottom of the tank, and a baffle for smoothing the flow of fluid through the ports positioned between the slot in the bottom of the tank and the ports in the tapered tube.
 11. Apparatus for electroplating a uniform metallic film on a substantially flat platable surface of a member to be plated, comprising: a container for an electrolyte solution having an interior nonconductive surface defining a predetermined cross section for containing an electrolyte solution, a holder having a flat platable surface and an opening therein for receiving the member such that the flat surface of the member forms a continuous surface with the flat surface of the holder, the continuous surface being mounted in the contAiner at a right angle to said nonconductive surface and extending over essentially all of said predetermined cross section.
 12. Apparatus according to claim 11 including means for generating an electric field through the electrolyte solution, the shape of the container and the generating means applying a uniform electric field up to and normal to substantially all of the continuous surface extending across the cross section of solution.
 13. Apparatus as defined in claim 11 including means for securing the member to be plated within the opening in said holder.
 14. Apparatus as defined in claim 11 comprising means for passing clean electrolyte solution over at least a portion of the continuous surface including the flat platable surface of the member.
 15. Apparatus as defined in claim 11 wherein the member to be plated has opposing substantially flat platable surfaces and wherein said holder has opposing substantially flat platable surfaces, the member to be plated being mountable in the opening of said holder such that the opposing flat surfaces of the member form opposing continuous surfaces with the flat surfaces of the holder, the generating means generating said field to both of the opposing continuous surfaces.
 16. Apparatus as defined in claim 15 comprising means for passing clean electrolyte solution over at least a portion of both of the continuous surfaces including the flat platable surfaces of the member.
 17. Apparatus for electroplating a uniform metallic film on a substantially flat platable surface of a member to be plated, comprising: a container for an electrolyte solution having an interior surface for containing an electrolyte solution, spaced-apart positions existing along said interior surface for an electrode and a member to be plated, the interior nonconductive surface defining a substantially constant cross section in size and shape in between the electrode position and the member position for containing the electrolyte solution, an electrode having a flat surface, a holder having a flat platable surface and an opening therein for receiving the member to be plated such that the flat surface of the member forms a continuous surface with the flat surface of the holder, the continuous surface of said holder and the flat surface of said electrode being parallel to each other and mounted at the electrode and member positions, respectively, at right angles to said nonconductive surface and extending over essentially all of said cross section at the respective positions.
 18. Apparatus according to claim 17 wherein the said interior surface comprises two flat parallel sidewalls and a flat bottom normal to said sidewalls.
 19. Apparatus for electroplating a uniform metallic film on a substantially flat platable surface of a member to be plated, comprising: a container for an electrolyte solution having at least two parallel interior nonconductive sidewalls and a nonconductive bottom for containing the solution; an electrode having a flat surface; a holder having a flat platable surface and an opening therein for receiving the member to be plated such that the flat surface of the member forms a continuous surface with the flat surface of the holder; the continuous surface of said holder and the flat surface of said electrode being spaced apart parallel to each other and mounted in said container at right angles to said walls and bottom and extending essentially from wall to wall and to the bottom such that the platable surface of the member may be completely immersed in the solution.
 20. Apparatus according to claim 19 wherein said walls and bottom are arranged such that said flat electrode surface and said flat continuous surface covering said cross section are positioned in direct alignment.
 21. Apparatus for electroplating a uniform metallic film on a substantially flat platable surface of a member to be plated, comprising: a container for an electrolyte solution having a nonconductivE interior surface defining a predetermined rectangular cross section, in between an electrode position and a position for the member to be plated for confining an electrolyte solution; an electrode having a flat surface; a holder having a flat platable surface and an opening therein for receiving the member such that the flat surface of said member forms a continuous surface with the flat surface of said holder; said electrodes and holder being mounted in the interior of said container at the respective electrode and member positions parallel to each other and normal to said interior surface and both extending essentially from side to side and to the bottom of said rectangular cross section to thereby permit a uniform electric field to be generated in the solution over at least a portion of said continuous flat surface including the platable surface of the member.
 22. A member having a metallic film of uniform thickness and magnetic properties electrodeposited on a flat platable surface thereof in a fluid electrolyte solution contained so as to have a predetermined cross section in size and shape while the member is mounted in a holder having a flat platable surface continuous with and surrounding the flat platable surface of the member, the flat continuous surface extending over the cross section of fluid while a uniform electric field is generated through the electrolyte of predetermined cross section up to the continuous surface.
 23. Apparatus for electrodepositing a uniform metallic film on a substantially flat platable surface of a member to be plated, comprising: a tank having two opposing inner walls and a bottom wall of a nonconductive material adapted for containing an electrolyte solution; holder means having a substantially flat platable surface and an opening therein for receiving the member to be plated; means for supporting the member to be plated in the opening such that the platable surface of the member forms a substantially flat continuous surface with the platable surface of the holder; an electrode assembly having a substantially flat electrode surface; means mounting the holder means within the tank, the holder means extending a flat platable surface substantially normal to the opposing walls of the tank extending essentially from one of said walls to the other and to said bottom wall such that the platable surface of the member to be plated may be completely immersed in the electrolyte solution; and means mounting the electrode assembly within the tank, the electrode assembly extending a flat electrode surface from essentially one of said opposing walls of the tank to essentially the other and to the bottom wall and substantially parallel to the platable surface of the holder means.
 24. Apparatus as defined in claim 23 including means for electrically connecting the electrode assembly as an anode and the holder means and the member to be plated as a cathode including means for applying a current signal to the electrode assembly, the shape of the tank permitting a uniform parallel electric field to be formed between and substantially normal to the flat surfaces of the holder means and the electrode assembly.
 25. The apparatus defined in claim 23 including means for imparting relative movement between the holder and the electrolyte solution adjacent thereto.
 26. Apparatus for electrodepositing a uniform metallic film on a platable surface of a member to be plated comprising: a tank having two parallel sides and normal thereto a bottom which are formed of an electrically nonconductive material and being adapted for containing an electrolyte solution; rectangular-shaped holder means having a platable surface and an opening therein for receiving the member to be plated; means for supporting the member to be plated in the opening such that the platable surface of the member forms a substantially continuous surface with the platable surface of the holder means; a rectangular-shapeD electrode assembly having an electrode surface; means mounting the holder means in the tank normal to both sides and to the bottom; means mounting the electrode assembly in the tank normal to both sides and to the bottom; the electrode assembly and holder means being constructed such that the electrode surface and continuous surface extend essentially from one of the sides to the other and to the bottom of the tank.
 27. Apparatus as defined in claim 26 including means for developing an electric signal between the electrode assembly and the holder means thereby forming a uniform field substantially normal to the continuous surface.
 28. Apparatus defined in claim 26 including means for imparting relative movement between the holder means and the electrolyte solution adjacent thereto.
 29. Apparatus for electrodepositing a uniform metallic film on a substantially flat platable surface of a member to be plated, comprising: container means forming a bottom and normal thereto a pair of substantially parallel walls having opposing surfaces all of a nonconductive material; holder means having a pair of substantially flat platable surfaces and an opening therein for receiving the member to be plated; means for supporting the member to be plated in the opening such that the platable surfaces of the member forms substantially flat continuous surfaces with the platable surfaces of the holder; a pair of electrode assemblies each having a substantially flat electrode surface; means mounting the holder means normal to the parallel walls and to the bottom, the outer periphery of the platable surfaces extending essentially up to and following the contour of the parallel walls and the bottom; and means mounting the electrode assemblies on either side of the holder means normal to the parallel walls and the bottom, the outer periphery of the electrode surfaces extending essentially up to and following the contour of the parallel walls and the bottom.
 30. Apparatus according to claim 29 including means for developing an electric field between the electrode assemblies and the holder means thereby forming a uniform field normal to the continuous surfaces.
 31. Apparatus according to claim 29 including means for directing clean electrolytic solution over the flat surface of the holder means between the holder means and the electrode assembly, the electrolyte solution containing ions of the metal to be electrodeposited, the electrolytic solution in the container means passing over the member to be plated.
 32. Apparatus for electroplating a uniform metallic film on a substantially flat platable surface of a member to be plated having an outer periphery of a first size and shape, comprising: a container for an electrolyte solution having an interior nonconductive surface defining a predetermined interior cross section having an outer periphery of a second size and shape for containing an electrolyte solution, a holder having a flat platable surface and an opening therein of substantially the same size and shape as the outer periphery of said member, the flat surface of the member forming a continuous surface with the flat surface of the holder, when mounted in said opening, the continuous surface of said holder being mounted in the container at a right angle to said nonconductive surface and extending over essentially all of said predetermined cross section to permit a uniform electric field to be applied in the solution up to and normal to substantially all of the continuous surface in the solution.
 33. Apparatus for electroplating a uniform metallic film on a substantially flat platable surface of a member to be plated having an outer periphery of a first size and shape, comprising: a container for an electrolyte solution having an interior nonconductive surface defining a predetermined interior cross section having an outer periphery of a second size and shape for containing an electrolyte solution, a holder haviNg a flat platable surface and an opening therein of substantially the same size and shape as the outer periphery of said member, the flat surface of the member forming a continuous surface with the flat surface of the holder, when mounted in said opening, the continuous surface of said holder being mounted in the container at a right angle to said nonconductive surface and extending over essentially all of said predetermined cross section, and means for generating an electric field through the electrolyte solution, the shape of the container and the generating means causing a uniform electric field to be applied in the solution up to and normal to substantially all of the continuous surface in the solution.
 34. Apparatus for electroplating a uniform metallic film on a substantially flat platable surface of a member to be plated, the member having an outer periphery of a first size and shape, the apparatus comprising: a tank including two sides and a bottom having a cross-sectional shape or size different from that of the outer periphery of the member to be plated, the tank being adapted for containing an electrolyte solution; holder means having a flat platable surface and an opening therein of substantially the same size and shape as the member to be plated, the holder means having an outer periphery of substantially the same shape as the cross-sectional shape of the sides and bottom of the tank and dimensioned to extend essentially from side to side and to the bottom of the tank; means for supporting the member to be plated in the opening such that the platable surface of the member forms a substantially continuous surface with the platable surface of the holder means; an electrode assembly having a substantially flat electrode surface and an outer periphery of substantially the same shape as the cross-sectional shape of the sides and bottom of the tank and extending essentially from side to side and to the bottom of the tank; means supporting the holder means and electrode assembly spaced apart and parallel to each other in said tank and substantially normal to the sides and to the bottom of said tank.
 35. Apparatus according to claim 34 including means for electrically connecting the electrode assembly as an anode and the member to be plated and the holder means as a cathode, the shape of the sides and bottom permitting a uniform electric field to be formed over substantially all of the continuous surface.
 36. A process for electroplating a metallic film of uniform thickness on a flat platable surface of a member to be plated, comprising the steps of: positioning the member to be plated in a holder such that the flat platable surface is surrounded by and forms an integral portion of a larger flat, substantially continuous, platable surface with the holder; immersing the flat platable surface in an electrolyte solution which is contained within a predetermined cross section such that the larger flat platable surface extends over essentially all of said cross section of solution; and generating a uniform electric field through the electrolyte solution up to and normal to substantially all of said larger flat continuous platable surface which is extending over said cross section of solution.
 37. A process as defined in claim 36 wherein the step of generating includes the step of positioning an electrode in the contained solution which extends over essentially all of said cross section of solution.
 38. A process as defined in claim 37 wherein the electrode and larger flat continuous platable surface are aligned parallel with respect to each other.
 39. A process as defined in claim 38 wherein the solution is contained within substantially the same cross section in between said electrode and said larger flat continuous platable surface.
 40. A process for electroplating a metallic film of uniform thickness on a flat platable surface of a member to be plated, comprising the steps of: positioning the mEmber to be plated in an opening in a holder having a substantially flat rectangular platable surface such that the flat platable surface of the member is surrounded by and forms an integral portion of a larger flat, substantially continuous, platable surface with the holder; containing an electrolyte solution within a rectangular cross section of substantially the same size and shape as said larger flat rectangular platable surface; immersing said continuous platable surface in said contained solution extending the larger flat continuous platable surface over essentially all of said cross section of solution; and generating a uniform electric field through the electrolyte solution up to and normal to substantially all of said larger flat continuous platable surface which is extending over said cross section of solution.
 41. A process for simultaneously electroplating metallic films of uniform thickness on opposing flat platable surfaces of a member to be plated, comprising the steps of: positioning the member within a holder having opposing flat platable surfaces such that the flat opposing surfaces of the member form part of larger continuous flat surfaces with the opposing surfaces of the holder; immersing the flat platable surfaces in an electrolyte solution which is contained within a predetermined cross section such that the larger flat platable surfaces extend over essentially all of said cross section of solution; and generating a uniform electric field through the electrolyte solution up to and normal to substantially all of said larger flat continuous platable surfaces which are extending over said cross section of solution.
 42. A process as defined in claim 41 wherein the step of generating includes the step of positioning electrodes in said solution on opposite sides of said holder both electrodes extending surfaces over essentially all of said cross section of solution.
 43. A process as defined in claim 42 wherein the electrodes and larger flat continuous platable surfaces are aligned parallel with respect to each other.
 44. A process as defined in claim 42 wherein the solution is contained within substantially the same cross section in between said electrodes and said larger flat continuous platable surfaces.
 45. Apparatus for electroplating a uniform metallic film on a substantially flat platable surface of a member, comprising: a container having an interior nonconductive surface for containing an electrolyte solution in a substantially right cylindrical volume in between first and second electrode positions, first and second substantially parallel electrodes respectively positioned at said first and second positions and extending substantially normal to said nonconductive surface over substantially all of the cross section of said volume thereby enabling a substantially uniform electric field to be generated throughout the solution between the electrodes, and a platable holder constructed for mounting said member and having a substantially flat electroplatable surface, said electroplatable surfaces of said holder and said member being electrically connected together and comprising part of a larger platable surface comprising said first electrode.
 46. Apparatus according to claim 45 wherein said holder has an opening for receiving said member and said flat electroplatable surface is positioned in substantially the same plane as said flat platable surface of said member.
 47. Apparatus according to claim 46 wherein said holder comprises a clamping member for bridging said member and holder and extending around said member to be plated.
 48. Apparatus according to claim 46 wherein said holder comprises an inner platable surface immediately surrounding said member in substantially the same plane as the platable surface of said member and an outer surface extending around said inner surface in a different plane.
 49. Apparatus according to claim 48 wherein said holder comprises a removable adapter which eXtends around said member and which includes said inner surface.
 50. Apparatus according to claim 49 wherein said adapter has a further surface extending around said inner surface in the same plane as said outer surface.
 51. Apparatus according to claim 50 including first and second electrically conductive clamping members extending respectively around the outer edges of said member and said further surface of said adapter for electrically and mechanically interconnecting said member to said inner surface and said further surface to said outer surface.
 52. Apparatus according to claim 50 wherein said adapter comprises an inclined surface at an oblique angle to said inner and outer surfaces for providing a transition between the different planes.
 53. Apparatus according to claim 50 wherein said member and said opening are round and said adapter is ring-shaped.
 54. Apparatus according to claim 46 wherein said member has an opening therein and wherein said first electrode additionally comprises an electroplatable member electrically and mechanically connected to said member in the opening thereof.
 55. Apparatus according to claim 45 wherein said member has opposing substantially flat parallel platable surfaces and wherein the container contains the electrolyte solution in said right cylindrical volume to a third position on the opposite side of said first position from said second position, a third electrode parallel to said first electrode and extending substantially normal to said nonconductive surface over substantially all of the cross section of said volume.
 56. Apparatus according to claim 55 comprising means for applying plating currents between said first and second electrodes and between said first and third electrodes.
 57. Apparatus according to claim 56 wherein said means for applying plating currents comprises means for independently regulating the plating currents between said second and first electrodes and between said third and first electrodes.
 58. Apparatus according to claim 45 including a narrow nonconductive member interposed between said electroplatable surfaces of said member and of said holder.
 59. Apparatus according to claim 58 wherein said nonconductive member extends above at least one of said electroplatable surfaces.
 60. Apparatus for electroplating a uniform metallic film on a substantially flat platable surface of a member having a predetermined peripheral configuration, comprising: a container having an interior nonconductive surface defining a substantially right cylindrical volume for containing an electrolyte solution in between first and second electrode positions, the cross-sectional configuration of said volume being different from the predetermined configuration of said member, first and second substantially parallel electrodes respectively positioned at said first and second positions, said first and second electrodes extending substantially normal to said nonconductive surface across substantially all of the cross section of said volume, said first electrode comprising a holder having a platable surface and having an opening of substantially the same configuration as said predetermined peripheral configuration of said member and adapted for receiving said member, said first electrode having a platable surface comprising the platable surface of said holder extending from around said opening across substantially all of the cross section of said volume enabling a substantially uniform electrical field to be generated throughout the solution between the electrodes when said member is mounted therein.
 61. Apparatus according to claim 60 comprising a clamping member for securing said member in the opening of said holder.
 62. Apparatus according to claim 60 wherein said holder comprises an inner platable surface immediately surrounding said opening in substantially the same plane as the platable surface of said member when mounted therein and an outer surface around said inner surface positionEd in a different plane.
 63. Apparatus according to claim 62 wherein said holder comprises a removable adapter which surrounds said opening and which includes said inner surface.
 64. Apparatus according to claim 63 wherein said adapter has a further surface around said inner surface in the same plane as said outer surface.
 65. Apparatus according to claim 64 including first and second electrically conductive clamping members extending respectively around the outer edges of said opening and said further surface of said adapter for electrically and mechanically interconnecting said member to said inner surface and said further surface to said outer surface.
 66. Apparatus according to claim 64 wherein said adapter comprises an inclined platable surface at an oblique angle to said inner and outer surfaces for providing a transition between the surfaces at different planes.
 67. Apparatus according to claim 64 wherein the peripheral configuration of said member and said opening are round and said adapter is ring-shaped.
 68. Apparatus according to claim 45 wherein said member has opposing substantially flat parallel platable surfaces and wherein the container contains the electrolyte solution in the substantially right cylindrical volume to a third position on the opposite side of said first position from said second position, and a third electrode parallel to said first electrode and extending substantially normal to said nonconductive surface across substantially all of the cross section of said volume.
 69. Apparatus according to claim 60 wherein said nonconductive surface comprises two flat and parallel walls and a bottom normal to said sides.
 70. A member having a metallic film of uniform thickness and magnetic properties electrodeposited on a flat platable surface thereof in a fluid electrolyte solution contained so as to have a substantially right angle cylindrical volume while the member is mounted on a holder therefor having a platable surface, said surfaces of said member and holder forming part of a larger platable surface extending over substantially all of the cross section of said volume while a uniform electric field is generated through the solution normal to and up to the larger surface.
 71. A process for electroplating a metallic film of uniform thickness on a flat platable surface of a member, comprising the steps of: positioning the member to be plated in a holder having a platable surface such that the flat platable surface of the member forms a portion of a larger platable surface with the holder; immersing the larger platable surface in an electrolyte solution which is contained within a substantially constant cross section such that the larger platable surface extends over substantially all of said cross section of solution; and generating a uniform electric field through the electrolyte solution up to and normal to substantially all of said larger platable surface.
 72. A process as defined in claim 71 comprising the step of positioning an electrode in said electrolyte solution substantially parallel to the larger platable surface and extending substantially continuously over all of said cross section of solution, containing the electrolyte solution in a cylinder having an axis perpendicular to both said electrode and larger platable surface.
 73. A process as defined in claim 70 wherein said cross section is substantially rectangular.
 74. A process for simultaneously electroplating metallic films of uniform thickness on opposing flat platable surfaces of a member to be plated, comprising the steps of: positioning the member within a holder having opposing flat platable surfaces such that the flat opposing surfaces of the member form part of larger platable surfaces with the opposing surfaces of the holder; immersing the flat platable surfaces in an electrolyte solution which is contained within a substantially constant cross section such that the larger platable surfaces extend over substantially all of said cross section of solution; and generating a uniform electric field through the electrolyte solution up to and normal to substantially all of said larger platable surfaces which are extending over said cross section of solution.
 75. A process as defined in claim 74 comprising the step of positioning a pair of electrodes in said electrolyte solution on either side of and substantially parallel to the larger platable surfaces and extending substantially continuously over all of said cross section of solution, containing the electrolyte solution in a cylinder having an axis perpendicular to both of said electrodes and to said larger platable surfaces. 